The SD300 has a built-in capability to build an functional Test Part using a minimum of consumables (less than $3 of total materials) which can be folded and snapped together into a neat little pyramid. Most users probably accumulate plenty of these parts from testing the printer after cleaning, servicing, and routine operations.

I've watched friends and guests toying with these little pyramids. Often, they try to stack them to form a larger pyramid, but it just doesn't work.
It occurred to me to design a simple part that can be
combined with the test parts to build a larger pyramid, like the one pictured below. It's sort of like a "missing piece" for the larger pyramid.

In fact, my extra piece
looks just like the standard test part...at first glance. It's foldable sheet of four triangles, like the test part, but the edges are chamfered at different angles and there are other differences.

This shape forms very-narrow channels during printing, which has the disadvantage of leaving hair-thin strands of support material that must be peeled away. I've successfully cleared the waste material from every part I built so far, but it takes a bit more effort than usual!

I added a triangular hole to the new part to help distinguish it from the ordinary test parts. As shown here, it doesn't quite fold like the regular test part.

I soon found the hole was a convenient feature to help disassemble the parts, so I designed a version of the standard SD300 Test Part with a round hole to reach inside and pop it apart. A complete puzzle set consists of one Mizzing Piece part (triangular hole, at right) and five standard test parts or my equivalent (round holes, at left).

I posted the Mizzing Piece STL at
Thingiverse